For thousands of years, ceramic has been generally produced from naturally occurring ceramic materials. Only since about ten years ago, ceramic materials and articles with special properties to meet specific needs have been manufactured from industrially produced materials. Novel ceramic materials are being developed continuously to meet world wide demand. This is because articles made of ceramic are resistant to corrosion, oxidation, peeling, aging and high temperatures. Ceramic articles also possess good hardness characteristics and other properties which are not found in articles made of comparable materials.
It is known that black articles rapidly absorb light and heat energy. Moreover, black articles emit infrared raidation when heated. Thus, black pigmented ceramic materials are desirable for use as absorbing and/or emitting elements for transforming heat energy into ligh energy or vice versa.
Heretofore, black pigments suitable for production of colored ceramic materials are usually made of the oxides of manganese, cobalt and nickel. These compounds are very expensive, making it difficult to produce black ceramic articles in large quantities. Therefore, up to the present, infrared absorbing or emitting elements have been made by coating a layer of an infrared radiating or absorbing material onto a substrate such as metals, ceramics made from silicon carbide or zircon sand, or plastics. However, these coating processes are complex and present many problems, such as, aging or peeling off of the coating layer. In addition, the coating processes are very expensive.
Therefore, for many years it has been the objective of many to produce low cost black ceramic materials for the production of articles with a high rate of infrared absorption and radiation. It has been found unexpectedly that some industrial wastes and natural ores can be used to this purposes.